1. Technical Field
The present disclosure is directed to advantageous valve prosthesis systems and associated methods/systems for placement of a heart valve prosthesis and, more particularly, to a mitral valve prosthesis that is adapted for secure and aligned placement relative to a heart annulus and associated methods/systems for placement thereof.
2. Background Art
Heart valve regurgitation occurs when the heart valve does not close completely as a result of disease or injury. Mitral regurgitation due to ischemic and degenerative (prolapse) disease has been shown to contribute to left ventricular dilation and dysfunction due to remodeling, and is associated with increased rates of cardiac events and death. Currently, malfunctioning heart valves may be replaced with biologic or mechanical prostheses through open-heart surgery with the attendant significant risk of death, stroke, infection, bleeding, and complications due to the use of general anesthesia and cardiopulmonary bypass.
Based on the success of percutaneous balloon valvuplasty for mitral stenosis, investigators have explored other alternative methods to treat valvular heart disease without surgery. For example, Cribier et al. describe a balloon-expandable stent to which a biologic valve prosthesis is sewn. (See, “Percutaneous Transcatheter Implantation of an Aortic Valve Prosthesis for Calcific Aortic Stenosis,” Circulation, Dec. 10, 2002, pages 3006-3008.) The Cribier device is utilized to treat calcific aortic stenosis. Bonhoeffer et al. describe a similar stent approach with a bovine venous (jugular) valve inserted to treat pulmonic valve disease. (See, “Percutaneous Insertion of the Pulmonary Valve,” Journal of the American College of Cardiology, Vol. 39, No. 10, May 15, 2002, pages 1664-1669.) Others are developing repair techniques for mitral valve disease that involve placing a clip on the mitral leaflets (U.S. Pat. No. 6,629,534), cinching the mitral annulus from the coronary sinus (U.S. Pat. No. 6,537,314), or deploying an inflatable heart valve that is mechanically held in place (U.S. Pat. No. 5,554,185).
Norred (U.S. Pat. No. 6,482,228) discloses a percutaneous aortic valve replacement in which a heart valve prosthesis having ribs and a circular elastomeric canopy is folded for insertion into a catheter for delivery to the implantation region without surgery. Once in the ascending aorta, the body and leaflets of the heart valve prosthesis are opened like an umbrella by pulling on a central column of suture-like members. Hinge joints are used to create a miniature umbrella. However, the aortic valve prosthesis is anchored using a stent system that is extended in the ascending aorta to anchor the valve in the aortic channel above the biologic aortic valve. The suture-like members used to open the umbrella structure are deployed as part of the stent system. Such a design is not amenable to placement of the heart valve prosthesis at the location of the biologic valve.
Other stented heart valve prostheses are described in the art in which the anchoring system is a passive one that requires either balloon expandable stents or a self-expanding stent design. For example, such stented designs are described in U.S. Pat. No. 6,454,799, US 2002/0138138, U.S. Pat. Nos. 6,582,462, 6,458,153, 6,425,916, and 5,855,601. It will be appreciated that once these stented heart valve prostheses are deployed, they cannot be repositioned, refolded, or easily removed. Furthermore, the rigidity of the stent as it is deployed in calcified positions may allow for regurgitation around the outside of the stent, as has been seen in the early aortic valve deployments which utilize this design. It is also difficult to position these designs as one has to inflate a balloon in a moving column of blood while the heart is beating and one only gets one chance to accurately deploy it.
An additional difficulty occurs when deploying a stented heart valve in an annulus that is not thickened by calcium. The stent design lends itself slightly better to the aortic position where the height of the annulus has been increased and the width thickened by the presence of calcium in calcific aortic stenosis. However, when calcium is not present, as in other causes of aortic valve disease and in the mitral position, the stent may be difficult to anchor on the relatively thin annulus. Furthermore, the nature by which the stent folds on a balloon and then expands with plastic deformability limits the ratio of its initial to final size such that it will, by necessity, have a fairly large profile making percutaneous insertion via catheter more difficult in a valve annulus with a large diameter that has not been reduced by calcium deposition.
Herrmann et al. (US 2007/0016286) disclose a percutaneously inserted bistable heart valve prosthesis that may be folded inside a catheter for delivery to the patient's heart for implantation. The heart valve has an elastic annular ring, a body member having a plurality of legs, each leg connecting at one end to the annular ring, claws that are adjustable from a first position to a second position by application of external force so as to allow ingress of surrounding heart tissue into the claws in the second position, and leaflet membranes connected to the annular ring, the body member and/or the legs. The disclosed leaflet membranes have a first position for blocking blood flow therethrough and a second position for allowing blood flow therethrough. The heart valve is designed such that upon removal of the external force, the claws elastically revert to the first position so as to grip the heart tissue positioned within the claws, thereby holding the heart valve in place. The body member and claws may be integrated into a one-piece design. The heart valve so designed may be used as a prosthesis for the mitral valve, aortic valve, pulmonary valve, or tricuspid valve by adapting the annular ring to fit in a respective mitral, aortic, pulmonary, or tricuspid valve opening of the heart.
Machold et al. (US 2004/0127982) disclose an implant that is sized and configured to attach to the annulus of a dysfunctional heart valve. In use, the implant extends across the major axis of the annulus above and/or along the valve annulus. The implant reshapes the major axis dimension and/or other surrounding anatomic structures and is intended to restore a more functional anatomic shape and tension. Machold et al. contemplate a pair of struts that are joined by a rail and that carry other structures to enhance the anchorage and stabilization of the implant in the heart valve annulus. The anchoring mechanisms may be located below the plane of the annulus to engage infra-annular heart tissue adjoining the annulus in the ventricle and/or may be located at or above the plane of the annulus, to engage tissue on the annulus or in the atrium. Machold et al. further disclose that the struts may be used to simply locate the implant in the valve, imparting little or no force on their own. In this arrangement, the annulus reshaping forces of the Machold design emanate from the rail(s) above the commissures.
Under image guidance, the Machold et al. strut on the leading end of the implant is freed from a sheath and seated retrograde in the posterior commissure of the valve annulus. Anchoring structures or mechanisms associated with the strut are also placed into contact with adjoining tissue below and/or above the plane of the annulus. As shown in FIG. 25B, the delivery catheter maintains force on the leading strut within the posterior commissure as the sheath is withdrawn in line with the coaptation line in a posterior-to-anterior direction along the coaptation line. Similar structures for positioning an implant relative to an annulus are disclosed by Vazquez et al. (U.S. Pat. No. 6,287,339).
Despite efforts to date, a need remains for an improved heart valve prosthesis design that allows a low profile for insertion via a catheter but, in the absence of a balloon or stent, transforms to a large profile once deployed. A heart valve prosthesis design is also desired that can be deployed, folded, removed, and then redeployed so as to increase the safety as well as the preciseness of prosthesis deployment. Still further, a need remains for heart valve prosthesis design(s) that may be effectively aligned and/or oriented relative to the heart and, most desirably, is substantially self-aligning and/or self-orienting with respect thereto. Reliable and effective deployment systems and methods for such advantageous heart valve prostheses are also needed.
These and other needs are addressed by the disclosed prosthesis designs and deployment systems/methodologies, as will be apparent from the detailed description which follows.